U.S. patent number 11,139,547 [Application Number 16/631,544] was granted by the patent office on 2021-10-05 for tunable bandpass filter and method of forming the same.
This patent grant is currently assigned to NEC CORPORATION. The grantee listed for this patent is NEC Corporation. Invention is credited to Takahiro Miyamoto, Norihisa Shiroyama.
United States Patent |
11,139,547 |
Miyamoto , et al. |
October 5, 2021 |
Tunable bandpass filter and method of forming the same
Abstract
A tunable bandpass filter (1A) includes a waveguide (11); a
plurality of resonators (12) housed in the waveguide (11) and
arranged in the lengthwise direction of the waveguide (11); a
coupling member (13) disposed between two adjacent resonators (12);
a ridge member (14) extending in the lengthwise direction of the
waveguide (11) and connected to one end of the coupling member
(13); and a dielectric plate (17) extending in the lengthwise
direction of the waveguide (11), disposed adjacent to the plurality
of resonators (12) in a direction orthogonal to the lengthwise
direction of the waveguide (11), and movable in the direction
orthogonal to the lengthwise direction of the waveguide (11).
Inventors: |
Miyamoto; Takahiro (Tokyo,
JP), Shiroyama; Norihisa (Kanagawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NEC Corporation |
Tokyo |
N/A |
JP |
|
|
Assignee: |
NEC CORPORATION (Tokyo,
JP)
|
Family
ID: |
65015402 |
Appl.
No.: |
16/631,544 |
Filed: |
June 1, 2018 |
PCT
Filed: |
June 01, 2018 |
PCT No.: |
PCT/JP2018/021105 |
371(c)(1),(2),(4) Date: |
January 16, 2020 |
PCT
Pub. No.: |
WO2019/017085 |
PCT
Pub. Date: |
January 24, 2019 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200176842 A1 |
Jun 4, 2020 |
|
Foreign Application Priority Data
|
|
|
|
|
Jul 20, 2017 [JP] |
|
|
JP2017-140560 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01P
1/20336 (20130101); H01P 1/207 (20130101); H01P
11/007 (20130101); H01P 1/2084 (20130101) |
Current International
Class: |
H01P
1/208 (20060101); H01P 11/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
62-202601 |
|
Sep 1987 |
|
JP |
|
2013-93811 |
|
May 2013 |
|
JP |
|
2016-119531 |
|
Jun 2016 |
|
JP |
|
2018/021105 |
|
Jul 2018 |
|
JP |
|
2010/073554 |
|
Jul 2010 |
|
WO |
|
Other References
International Search Report for PCT/JP2018/021105 dated Jul. 17,
2018 (PCT/ISA/210). cited by applicant.
|
Primary Examiner: Pascal; Robert J
Assistant Examiner: Glenn; Kimberly E
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
The invention claimed is:
1. A tunable bandpass filter comprising: a waveguide; a plurality
of resonators housed in the waveguide and arranged in a lengthwise
direction of the waveguide; a coupling member disposed between two
adjacent resonators among the plurality of resonators; a ridge
member extending in the lengthwise direction of the waveguide and
connected to one end of the coupling member; and a dielectric plate
extending in the lengthwise direction of the waveguide, disposed
adjacent to the plurality of resonators in a direction orthogonal
to the lengthwise direction of the waveguide, and movable in the
direction orthogonal to the lengthwise direction of the waveguide,
wherein one end of each of the plurality of resonators is connected
to an inner wall of the waveguide, and another end of each of the
plurality of resonators is an open end.
2. The tunable bandpass filter according to claim 1, wherein the
ridge member is disposed on another inner wall of the
waveguide.
3. The tunable bandpass filter according to claim 1, wherein the
plurality of resonators, the coupling member, and the ridge member
are plate-like members located in the same plane.
4. The tunable bandpass filter according to claim 3, wherein the
waveguide is divided into two members along the plane with a
plate-like conductor plate being sandwiched by the two members, and
the plurality of resonators, the coupling member, and the ridge
member are formed integrally in the conductor plate.
5. The tunable bandpass filter according to claim 1, wherein a
passband is changed by changing a distance between the plurality of
resonators and the dielectric plate.
6. A method of forming a tunable bandpass filter, the method
comprising: housing, in a waveguide, a plurality of resonators
arranged in a lengthwise direction of the waveguide; disposing a
coupling member between two adjacent resonators among the plurality
of resonators; disposing a ridge member extending in the lengthwise
direction of the waveguide and connected to one end of the coupling
member; and disposing a dielectric plate adjacent to the plurality
of resonators in a direction orthogonal to the lengthwise direction
of the waveguide, the dielectric plate extending in the lengthwise
direction of the waveguide and being movable in the direction
orthogonal to the lengthwise direction of the waveguide, wherein
one end of each of the plurality of resonators is connected to an
inner wall of the waveguide, and another end of each of the
plurality of resonators is an open end.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a National Stage of International Application
No. PCT/JP2018/021105 filed Jun. 1, 2018, claiming priority based
on Japanese Patent Application No. 2017-140560 filed Jul. 20, 2017,
the disclosure of which is incorporated herein in its entirety by
reference.
TECHNICAL FIELD
The present disclosure relates to a tunable bandpass filter and a
method of forming the tunable bandpass filter.
BACKGROUND ART
For communication devices that transmit and receive signals with
the use of a microwave band or a millimeter-wave band, there is
known a bandpass filter that passes only a signal in a desired
frequency band and removes an unwanted frequency component.
Nowadays, there is an increasing demand that the passband of a
bandpass filter be changed from the outside. An example of a
tunable bandpass filter whose passband can be changed from the
outside is disclosed in Patent Literature 1.
In the tunable bandpass filter disclosed in Patent Literature 1, a
metal plate is sandwiched by a waveguide divided into half along a
horizontal plane, and a plurality of capacitive fins are arranged
in the metal plate in the lengthwise direction of the waveguide. A
dielectric plate is disposed inside the waveguide along the
lengthwise direction of the metal plate, and this dielectric plate
is configured to be movable in the direction of the metal
plate.
With the tunable bandpass filter disclosed in Patent Literature 1
and configured as described above, the center frequency of the
passband can be changed by changing, from the outside, the position
of the dielectric plate, that is, the distance between the
dielectric plate and the metal plate.
CITATION LIST
Patent Literature
Patent Literature 1: Japanese Unexamined Patent Application
Publication No. 2016-119531
SUMMARY OF INVENTION
Technical Problem
As described above, in the tunable bandpass filter disclosed in
Patent Literature 1, the plurality of capacitive fins are formed
and arranged in the metal plate sandwiched by the waveguide divided
into half, and the distance between the dielectric plate and the
metal plate is changed from the outside. Thus, the center frequency
of the passband can be changed. Patent Literature 1 further
indicates that the capacitive fins contribute to suppressing a
change in the coupling coefficient between resonators that could
occur when the center frequency of the passband is changed.
However, according to FIG. 5 of Patent Literature 1, the coupling
coefficient changes greatly dependent on the frequency especially
in a high frequency band. In general, when the coupling coefficient
changes, the bandwidth of the passband changes.
Therefore, it is conceivable that, with the tunable bandpass filter
disclosed in Patent Literature 1, changing the center frequency of
the passband causes the coupling coefficient between the resonators
to change and this also causes the bandwidth of the passband to
change.
The present disclosure is directed to solving the above problem and
to providing a tunable bandpass filter that can suppress a change
in the bandwidth of a passband that could occur when the center
frequency of the passband is changed and providing a method of
forming such a tunable bandpass filter.
Solution to Problem
In one aspect, a tunable bandpass filter includes a waveguide;
a plurality of resonators housed in the waveguide and arranged in a
lengthwise direction of the waveguide;
a coupling member disposed between two adjacent resonators;
a ridge member extending in the lengthwise direction of the
waveguide and connected to one end of the coupling member; and
a dielectric plate extending in the lengthwise direction of the
waveguide, disposed adjacent to the plurality of resonators in a
direction orthogonal to the lengthwise direction of the waveguide,
and movable in the direction orthogonal to the lengthwise direction
of the waveguide.
In one aspect, a method of forming a tunable bandpass filter
includes
housing, in a waveguide, a plurality of resonators arranged in a
lengthwise direction of the waveguide;
disposing a coupling member between two adjacent resonators;
disposing a ridge member extending in the lengthwise direction of
the waveguide and connected to one end of the coupling member;
and
disposing a dielectric plate adjacent to the plurality of
resonators in a direction orthogonal to the lengthwise direction of
the waveguide, the dielectric plate extending in the lengthwise
direction of the waveguide and being movable in the direction
orthogonal to the lengthwise direction of the waveguide.
Advantageous Effects of Invention
The above aspects can advantageously provide a tunable bandpass
filter that can suppress a change in the bandwidth that could occur
when the center frequency of the passband is changed and a method
of forming such a tunable bandpass filter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view illustrating a configuration example
of a tunable bandpass filter according to a first embodiment;
FIG. 2 is a top view illustrating a configuration example of the
tunable bandpass filter according to the first embodiment;
FIG. 3 is a side view illustrating a configuration example of the
tunable bandpass filter according to the first embodiment;
FIG. 4 is an enlarged top view of the vicinity of second-stage and
third-stage resonator plates illustrated in FIG. 2;
FIG. 5 is a graph illustrating an example of a coupling coefficient
in the tunable bandpass filter according to the first
embodiment;
FIG. 6 is a graph illustrating an example of filter characteristics
of the tunable bandpass filter according to the first
embodiment;
FIG. 7 is a perspective view illustrating a configuration example
of a tunable bandpass filter according to a second embodiment;
and
FIG. 8 is a top view illustrating a configuration example of the
tunable bandpass filter according to the second embodiment.
DESCRIPTION OF EMBODIMENTS
Hereinafter, with reference to the drawings, an embodiment of the
present disclosure will be explained. Further, specific numerical
values and the like stated in the following embodiments are merely
examples for facilitating understanding of the present disclosure,
and are not limited thereto.
(1) First Embodiment
FIGS. 1 to 3 are, respectively, a perspective view, a top view, and
a side view illustrating a configuration example of a tunable
bandpass filter 1A according to a first embodiment. FIG. 4 is an
enlarged top view of the vicinity of second-stage and third-stage
resonator plates 12-2 and 12-3 illustrated in FIG. 2. In FIG. 4, a
flap 17 is omitted.
As illustrated in FIGS. 1 to 4, the tunable bandpass filter 1A
according to the first embodiment includes a waveguide 11, four
resonator plates 12-1 to 12-4, three coupling plates 13-1 to 13-3,
a ridge plate 14, two input/output ports 15-1 and 15-2, a flap 17,
and two support rods 18-1 and 18-2. In the following, when the
resonator plates 12-1 to 12-4 are not particularly distinguished
from one another, the resonator plates 12-1 to 12-4 may be referred
to simply as the "resonator plate(s) 12." In a similar manner, the
coupling plates 13-1 to 13-3 may be referred to simply as the
"coupling plate(s) 13," the input/output ports 15-1 and 15-2 may be
referred to simply as the "input/output port(s) 15," and the
support rods 18-1 and 18-2 may be referred to simply as the
"support rod(s) 18." In addition, center conductors 16-1 and 16-2
in the input/output ports 15-1 and 15-2, described later, may be
referred to simply as the "center conductor(s) 16."
The tunable bandpass filter 1A according to the first embodiment is
a four-stage bandpass filter that includes the four resonator
plates 12-1 to 12-4. The number of the stages in the tunable
bandpass filter 1A is not limited to four and may be two or
more.
The waveguide 11 is a conductive rectangular waveguide that houses,
in its cavity, the resonator plates 12-1 to 12-4, the coupling
plates 13-1 to 13-3, the ridge plate 14, the flap 17, and so on.
The material of the waveguide 11 may be any metal having high
conductivity and is, for example, aluminum.
The resonator plates 12-1 to 12-4 are each a semi-coaxial resonator
constituted by a plate-like conductor. One ends (the positive side
ends in the y-direction) of the resonator plates 12-1 to 12-4 are
connected to the ridge plate 14, described later, and the other
ends (the negative side ends in the y-direction) are open ends
(i.e., not connected to any member). The resonator plates 12-1 to
12-4 are arranged in the lengthwise direction (x-direction) of the
waveguide 11 such that the side surfaces of the resonator plates 12
oppose each other. The resonator plates 12-1 to 12-4 operate so as
to resonate at a resonance frequency that is determined by their
shape, their length (y-direction), or the like.
The coupling plates 13-1 to 13-3 are each a coupling member
constituted by a conductor. One ends (the positive side ends in the
y-direction) of the coupling plates 13-1 to 13-3 are connected to
the ridge plate 14, described later, and the other ends (the
negative side ends in the y-direction) are connected to the inner
wall on the other side (the negative side inner wall in the
y-direction) of the waveguide 11. The coupling plates 13-1 to 13-3
may also be referred to as irises. The coupling plates 13-1 to 13-3
are each disposed between two adjacent resonator plates 12 such
that the side surfaces of the coupling plates 13 oppose the side
surfaces of the resonator plates 12. The coupling plates 13-1 to
13-3 are provided to suppress spurious (unwanted resonance).
The ridge plate 14 is a ridge member constituted by a conductor.
The ridge plate 14 extends in the lengthwise direction
(x-direction) of the waveguide 11, and a side surface of the ridge
plate 14 is connected to one of the inner walls (the positive side
inner wall in the y-direction) of the waveguide 11. The ridge plate
14 is connected to the one ends (the positive side ends in the
y-direction) of the resonator plates 12-1 to 12-4 and is connected
to the one ends (the positive side ends in the y-direction) of the
coupling plates 13-1 to 13-3. The ridge plate 14 is provided to
increase the coupling coefficient between two adjacent resonator
plates 12. It suffices that the length of the ridge plate 14 in the
x-direction be no less than the length that allows the ridge plate
14 to reach the resonator plates 12-1 and 12-4 at the respective
ends in the x-direction.
The input/output ports 15-1 and 15-2 are ports for inputting and/or
outputting a high-frequency signal. The input/output port 15-1 is
constituted by a coaxial line. The center conductor 16-1 of that
coaxial line is inserted, at one end (the negative side end in the
x-direction) of the waveguide 11, through a side surface (on the
positive side in the y-direction) of the waveguide 11 and connected
to the resonator plate 12-1 through electromagnetic coupling. The
input/output port 15-2 is constituted by a coaxial line. The center
conductor 16-2 of that coaxial line is inserted, at the other end
(the positive side end in the x-direction) of the waveguide 11,
through the side surface (on the positive side in the y-direction)
of the waveguide 11 and connected to the resonator plate 12-4
through electromagnetic coupling. The center conductors 16-1 and
16-2 are constituted by plate-like conductors. The input/output
ports 15-1 and 15-2 are not limited to the coaxial lines and may
each be constituted by a waveguide line. One of the input/output
ports 15-1 and 15-2 operates as an input port, and the other one
operates as an output port. For example, when the input/output port
15-1 operates as an input port and the input/output port 15-2
operates as an output port, a high-frequency signal is input to the
input/output port 15-1, and only a portion of that high-frequency
signal that is in a passband of the tunable bandpass filter 1A is
output from the input/output port 15-2.
The waveguide 11 is divided into two members along a horizontal
plane, and the two divided members sandwich a conductor plate. The
resonator plates 12-1 to 12-4, the coupling plates 13-1 to 13-3,
the ridge plate 14, the center conductors 16-1 and 16-2 of the
input/output ports 15-1 and 15-2, and so on are formed integrally
in the stated conductor plate. Accordingly, the resonator plates
12-1 to 12-4, the coupling plates 13-1 to 13-3, the ridge plate 14,
the center conductors 16-1 and 16-2, and so on are located in the
same plane (the horizontal plane in FIGS. 1 to 4).
Since the resonator plates 12-1 to 12-4, the coupling plates 13-1
to 13-3, the ridge plate 14, and the center conductors 16-1 and
16-2 of the input/output ports 15-1 and 15-2 are formed integrally
in the conductor plate sandwiched by the waveguide divided into
half as described above, these members are formed of the same
material. The material of the resonator plates 12-1 to 12-4, the
coupling plates 13-1 to 13-3, the ridge plate 14, and the center
conductors 16-1 and 16-2 may be any metal having high conductivity
and is, for example, copper. The resonator plates 12-1 to 12-4, the
coupling plates 13-1 to 13-3, the ridge plate 14, and the center
conductors 16-1 and 16-2 may each be constituted by an insulator,
such as plastics, having its surface plated with a metal having
high conductivity.
The flap 17 is a plate-like dielectric plate. The flap 17 extends
in the lengthwise direction (x-direction) of the waveguide 11 and
is disposed adjacent to the resonator plates 12-1 to 12-4 in a
direction (z-direction) orthogonal to the lengthwise direction of
the waveguide 11. A principal surface (a surface having the largest
area) of the flap 17 opposes principal surfaces of the resonator
plates 12-1 to 12-4. It suffices that the length of the flap 17 in
the x-direction be no less than the length that allows the flap 17
to overlap the input/output ports 15-1 and 15-2 at the respective
ends in the x-direction. The flap 17 is configured to be movable in
the z-direction. This configuration makes it possible to change the
position of the flap 17 in the z-direction, that is, the distance
between the resonator plates 12-1 to 12-4 and the flap 17.
Accordingly, with the tunable bandpass filter 1A according to the
first embodiment, the center frequency of the passband can be
changed by changing, from the outside, the distance between the
resonator plates 12-1 to 12-4 and the flap 17. The material of the
flap 17 may be any dielectric member having a relative permittivity
of .epsilon.r>1 and is, for example, alumina.
The support rods 18-1 and 18-2 are attached at the respective ends
of the flap 17 in the x-direction. The support rods 18-1 and 18-2
are displaced in the z-direction with the use of a stepping motor
(not illustrated) provided outside the tunable bandpass filter 1A,
and thus the flap 17 can be moved in the z-direction. The material
of the support rods 18-1 and 18-2 is, for example, zirconia. The
above-described method of moving the flap 17 with the use of the
support rods 18-1 and 18-2 is merely an example, this method is not
a limiting example.
As described above, in the tunable bandpass filter 1A according to
the first embodiment, the resonator plates 12-1 to 12-4 are
arranged in the lengthwise direction (x-direction) of the waveguide
11, and the coupling plates 13-1 to 13-3 are each disposed between
two adjacent resonator plates 12 to suppress spurious.
The coupling plates 13-1 to 13-3 have not only an effect of
suppressing spurious but also an effect of reducing the coupling
coefficient between two adjacent resonator plates 12. Therefore,
the presence of the coupling plates 13-1 to 13-3 helps reduce the
coupling coefficient.
The bandwidth of the passband is dependent on the coupling
coefficient, and as the coupling coefficient decreases, the
bandwidth decreases. Therefore, the decrease in the coupling
coefficient makes it impossible to obtain a desired bandwidth.
Accordingly, in the first embodiment, the ridge plate 14 that
extends in the lengthwise direction (x-direction) of the waveguide
11 is disposed, and the one ends (the positive side ends in the
y-direction) of the coupling plates 13-1 to 13-3 are connected to
the ridge plate 14. This configuration helps increase the coupling
coefficient between two adjacent resonator plates 12.
With reference to FIG. 5, the following description shows that the
effect of the ridge plate 14 can increase the coupling coefficient
between two adjacent resonator plates 12.
In the tunable bandpass filter 1A, the width W (x-direction) of the
three coupling plates 13-1 to 13-3 is varied. Aside from this, the
tunable bandpass filter 1A is configured in accordance with the
following conditions.
Width cav_y (y-direction) of waveguide 11: 5 [mm]
Height cav_z (z-direction) of waveguide 11: 8 [mm]
Height reso_y (y-direction) of resonator plate 12: 3.3 [mm]
Thickness reso_z (z-direction) of resonator plate 12: 0.3 [mm]
Height rid_y (y-direction) of ridge plate 14: 1 [mm]
Width fla_y (y-direction) of flap 17: 3.5 [mm]
Thickness fla_z (z-direction) of flap 17: 0.5 [mm]
Position fla_dz (z-direction) of flap 17: 1.8 [mm]
The position fla_dz of the flap 17 represents the distance between
the resonator plates 12-1 to 12-4 and the flap 17. The height
reso_y of the resonator plates 12 and the height rid_y of the ridge
plate 14 each represent the distance from the one inner wall (the
positive side inner wall in the y-direction) of the waveguide 11.
The thickness (z-direction) of each of the coupling plates 13, the
ridge plate 14, and the center conductors 16 of the input/output
ports 15 is equal to the thickness reso_z of the resonator plates
12.
FIG. 5 is a graph illustrating an example of the coupling
coefficient in the tunable bandpass filter 1A according to the
first embodiment. In FIG. 5, the horizontal axis represents the
width W [mm] (x-direction) of the coupling plates 13-1 to 13-3, and
the vertical axis represents the coupling coefficient k between two
adjacent resonator plates 12.
Herein, an index used for the bandwidth of the passband is a 3-dB
width index associated with S21 of the S-parameter. S21 represents
the pass characteristics of a high-frequency signal and indicates a
pass loss (also referred to as an insertion loss) with respect to
the frequency. The 3-dB width indicates a gap between the
frequencies at two points where S21 [dB] takes a value that is
smaller (greater in the negative direction) by 3 [dB] than a peak
value. Herein, 220 [MHz] is required as the 3-dB width. To achieve
3-dB width of 220 [MHz], the coupling coefficient k needs to
satisfy a lower limit value of k2=0.00794 and an upper limit value
of k1=0.0108.
FIG. 5 reveals that, in the first embodiment, the presence of the
ridge plate 14 can help achieve the coupling coefficient k of 0.012
at the minimum, which is sufficiently large. Therefore, as the
width W of the three coupling plates 13-1 to 13-3 is set to
W2=0.9496 [mm], the coupling coefficient k can satisfy the lower
limit value of k2=0.00794. Furthermore, as the width W is set to
W1=0.4519 [mm], the coupling coefficient k can also satisfy the
upper limit value of k1=0.0108.
Accordingly, it can be seen that, in the first embodiment, the
effect of the ridge plate 14 can help increase the coupling
coefficient k between two adjacent resonator plates 12, and this
can help obtain a desired bandwidth. The coupling coefficient k can
be further increased by further increasing the height rid_y of the
ridge plate 14.
In the first embodiment, the center frequency of the passband can
be changed by changing, from the outside, the distance between the
resonator plates 12-1 to 12-4 and the flap 17. Even when the center
frequency of the passband is changed, the effect of the ridge plate
14 can help suppress a change in the coupling coefficient between
two adjacent resonator plates 12, and this can help suppress a
change in the bandwidth of the passband.
With reference to Table 1 and FIG. 6, the following description
shows that, when the center frequency of the passband has been
changed, the effect of the ridge plate 14 can help suppress a
change in the coupling coefficient between two adjacent resonator
plates 12 in the first embodiment, and this can help suppress a
change in the bandwidth of the passband.
In this case, in the tunable bandpass filter 1A, the position
fla_dz (z-direction) of the flap 17 is varied. The width W
(x-direction) of the coupling plates 13-1 and 13-3 is set to 0.45
[mm], and the width W (x-direction) of the coupling plate 13-2 is
set to 0.95 [mm]. Aside from the above, the tunable bandpass filter
1A is configured in accordance with the conditions similar to those
in the case of FIG. 5.
Table 1 illustrates examples of the center frequency f0 [MHz] of
the passband, the difference .DELTA.f [MHz] in the center frequency
f0, the 3-dB width [MHz] of S21, and the coupling coefficient k
between two adjacent resonator plates 12 held when the position
fla_dz [mm] of the flap 17 is varied in the tunable bandpass filter
1A. In Table 1, the center frequency f0 [MHz] held when the
position fla_dz of the flap 17 is 2.5 [mm] serves as a reference
value, and .DELTA.f indicates the difference from that reference
value. A coupling coefficient k12 is a coupling coefficient between
the resonator plates 12-1 and 12-2, a coupling coefficient k34 is a
coupling coefficient between the resonator plates 12-3 and 12-4,
and a coupling coefficient k23 is a coupling coefficient between
the resonator plates 12-2 and 12-3.
TABLE-US-00001 TABLE 1 FLAP POSITION 3-dB COUPLING COUPLING fla_dz
f0 .DELTA.f WIDTH COEFFICIENT COEFFI- [mm] [MHz] [MHz] [MHz] k12 =
k34 CIENT k23 2.5 15005 -- 197 0.00968 0.00711 1.8 14675 330 203
0.010199 0.007491 1.4 14423 582 200 0.010223 0.007509 1.1 14146 859
202 0.010528 0.007733
FIG. 6 is a graph illustrating an example of filter characteristics
of the tunable bandpass filter 1A according to the first embodiment
(a simulation result from a high-frequency electric field
simulator). In FIG. 6, the horizontal axis represents the frequency
[GHz], and the vertical axis represents the reflection loss (the
return loss, S11 of the S-parameter) and the pass loss (S21 of the
S-parameter) [dB]. S11 represents the reflection characteristics of
a high-frequency signal and indicates the reflection loss with
respect to the frequency. S21 is as described above.
Table 1 and FIG. 6 reveal that, in the first embodiment, as the
position fla_dz of the flap 17 is changed, the center frequency f0
of the passband changes. Specifically, as the position fla_dz of
the flap 17 is raised, that is, as the flap 17 is moved further
away from the resonator plates 12-1 to 12-4, the center frequency
f0 of the passband increases. Meanwhile, it can be seen that, even
when the center frequency f0 of the passband has changed, little
change is observed in the 3-dB width and the coupling coefficients
k12, k34, and k23. Specifically, even when the position fla_dz of
the flap 17 is varied in a range of from 1.1 [mm] to 2.5 [mm], the
change in the 3-dB width is kept to 6 [MHz], the change in the
coupling coefficients k12 and k34 is kept to 0.000848, and the
change in the coupling coefficient k23 is kept to 0.000623.
Accordingly, it can be seen that, in the first embodiment, even
when the center frequency of the passband is changed, the effect of
the ridge plate 14 can help suppress a change in the coupling
coefficient between two adjacent resonator plates 12, and this can
help suppress a change in the bandwidth of the passband.
As described above, in the tunable bandpass filter 1A according to
the first embodiment, the resonator plates 12-1 to 12-4 are
arranged in the lengthwise direction (x-direction) of the waveguide
11, and the coupling plates 13-1 to 13-3 are each disposed between
two adjacent resonator plates 12. This configuration can suppress
spurious.
Furthermore, the ridge plate 14 that extends in the lengthwise
direction (x-direction) of the waveguide 11 is disposed, and the
one ends (the positive side ends in the y-direction) of the
coupling plates 13-1 to 13-3 are connected to the ridge plate 14.
This configuration can help increase the coupling coefficient
between two adjacent resonator plates 12. In addition, a change in
the coupling coefficient that could occur when the center frequency
of the passband is changed by moving the flap 17 can be suppressed,
and this can help suppress a change in the bandwidth of the
passband.
(2) Second Embodiment
FIGS. 7 and 8 are, respectively, a perspective view and a top view
illustrating a configuration example of a tunable bandpass filter
1B according to a second embodiment.
As illustrated in FIGS. 7 and 8, the tunable bandpass filter 1B
according to the second embodiment differs from the tunable
bandpass filter 1A according to the first embodiment described
above in terms of the position of the ridge plate 14.
Specifically, in the first embodiment described above, the ridge
plate 14 is disposed on the one inner wall (the positive side inner
wall in the y-direction) of the waveguide 11. In contrast, in the
second embodiment, the ridge plate 14 is disposed on the other
inner wall (the negative side inner wall in the y-direction) of the
waveguide 11.
Along with this change in the position of the ridge plate 14, the
one ends (the positive side ends in the y-direction) of the
coupling plates 13-1 to 13-3 are connected to the one inner wall
(the positive side inner wall in the y-direction) of the waveguide
11, and the other ends of the coupling plates 13-1 to 13-3 are
connected to the ridge plate 14. Meanwhile, the one ends (the
positive side ends in the y-direction) of the resonator plates 12-1
to 12-4 are connected to the one inner wall (the positive side
inner wall in the y-direction) of the waveguide 11, and the other
ends (the negative side ends in the y-direction) of the resonator
plates 12-1 to 12-4 are open ends.
Aside from the configuration described above, the second embodiment
is similar to the first embodiment, and thus any further
description will be omitted.
Although the position of the ridge plate 14 is different, the
second embodiment is similar in configuration to the first
embodiment in that the ridge plate 14 extends in the lengthwise
direction (x-direction) of the waveguide 11 and the coupling plates
13-1 to 13-3 are connected to the ridge plate 14. Accordingly, the
second embodiment provides an effect similar to that of the first
embodiment described above.
Thus far, the invention of the present application has been
described with reference to the foregoing embodiments, but the
invention of the present application is not limited to the
foregoing embodiments. Various modifications that a person skilled
in the art can appreciate can be made to the configurations and the
details of the invention of the present application within the
scope of the invention of the present application.
For example, in the foregoing embodiments, the resonators, the
coupling members, the ridge member, and the center conductors of
the input/output ports each have a plate-like shape, and this
provides an advantage in that these members can be formed
integrally in a single conductor plate. However, the shape of the
resonators, the coupling members, the ridge member, and the center
conductors of the input/output ports is not limited to a plate-like
shape. The shape of the resonators, the coupling members, the ridge
member, and the center conductors of the input/output ports may be,
for example, a circular column, a rectangular parallelepiped, or
the like.
REFERENCE SIGNS LIST
1A, 1B TUNABLE BANDPASS FILTER 11 WAVEGUIDE 12-1 TO 12-4 RESONATOR
PLATE 13-1 TO 13-3 COUPLING PLATE 14 RIDGE PLATE 15-1, 15-2
INPUT/OUTPUT PORT 16-1, 16-2 CENTER CONDUCTOR 17 FLAP 18-1, 18-2
SUPPORT ROD
* * * * *